libc_init_static.cpp revision 38778e3b6c89689bbdd01f4a52ac88f02bf59783 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28/*
29 * libc_init_static.c
30 *
31 * The program startup function __libc_init() defined here is
32 * used for static executables only (i.e. those that don't depend
33 * on shared libraries). It is called from arch-$ARCH/bionic/crtbegin_static.S
34 * which is directly invoked by the kernel when the program is launched.
35 *
36 * The 'structors' parameter contains pointers to various initializer
37 * arrays that must be run before the program's 'main' routine is launched.
38 */
39
40#include <elf.h>
41#include <errno.h>
42#include <stddef.h>
43#include <stdint.h>
44#include <stdio.h>
45#include <stdlib.h>
46#include <sys/auxv.h>
47#include <sys/mman.h>
48
49#include "libc_init_common.h"
50#include "pthread_internal.h"
51
52#include "private/bionic_tls.h"
53#include "private/KernelArgumentBlock.h"
54
55// Returns the address of the page containing address 'x'.
56#define PAGE_START(x)  ((x) & PAGE_MASK)
57
58// Returns the address of the next page after address 'x', unless 'x' is
59// itself at the start of a page.
60#define PAGE_END(x)    PAGE_START((x) + (PAGE_SIZE-1))
61
62extern "C" int __cxa_atexit(void (*)(void *), void *, void *);
63
64static void call_array(void(**list)()) {
65  // First element is -1, list is null-terminated
66  while (*++list) {
67    (*list)();
68  }
69}
70
71static void apply_gnu_relro() {
72  ElfW(Phdr)* phdr_start = reinterpret_cast<ElfW(Phdr)*>(getauxval(AT_PHDR));
73  unsigned long int phdr_ct = getauxval(AT_PHNUM);
74
75  for (ElfW(Phdr)* phdr = phdr_start; phdr < (phdr_start + phdr_ct); phdr++) {
76    if (phdr->p_type != PT_GNU_RELRO) {
77      continue;
78    }
79
80    ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr);
81    ElfW(Addr) seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz);
82
83    // Check return value here? What do we do if we fail?
84    mprotect(reinterpret_cast<void*>(seg_page_start), seg_page_end - seg_page_start, PROT_READ);
85  }
86}
87
88__noreturn void __libc_init(void* raw_args,
89                            void (*onexit)(void) __unused,
90                            int (*slingshot)(int, char**, char**),
91                            structors_array_t const * const structors) {
92  KernelArgumentBlock args(raw_args);
93  __libc_init_tls(args);
94  __libc_init_common(args);
95
96  apply_gnu_relro();
97
98  // Several Linux ABIs don't pass the onexit pointer, and the ones that
99  // do never use it.  Therefore, we ignore it.
100
101  call_array(structors->preinit_array);
102  call_array(structors->init_array);
103
104  // The executable may have its own destructors listed in its .fini_array
105  // so we need to ensure that these are called when the program exits
106  // normally.
107  if (structors->fini_array != NULL) {
108    __cxa_atexit(__libc_fini,structors->fini_array,NULL);
109  }
110
111  exit(slingshot(args.argc, args.argv, args.envp));
112}
113